Angular Fringe Width — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Angular Fringe Width Used in Young's Double Slit Experiment (YDSE) to calculate the angular spacing of the interference pattern. The linear fringe width is defined as beta = (lambda D) / d, where D is distance to screen. The angular width is the ratio of linear fringe width to the distance from the slit to the screen: theta = beta / D. Substitute beta into the expression: theta = (lambda D) / (d D). D cancels out, leaving theta = lambda / d. Small angle approximation must hold (sin theta approx theta). Sources must be coherent. Light must be monochromatic. Slit separation d must be significantly larger than wavelength lambda. Mistaking angular fringe width for the angular width of the central maximum in diffraction (which is 2 lambda/a). Thinking angular width depends on the screen distance D; it is actually independent of D. Calculating in degrees without converting to radians first.